Flame retardant resin compositions

ABSTRACT

Flame retardant resin compositions are disclosed, comprising a thermoplastic condensation polymer selected from the group consisting of polyesters, polycarbonates and polyamides, a halogenated flame-retardant, and a rubber-occluded flame retardant synergist. The compositions possess superior stability in melt processing and improved flame retardancy and impact strength.

This invention relates to compositions moldable into flame retardantarticles comprising a condensation polymer, a halogenated additive, anda rubber-occluded flame retardant synergist and to the molded articlesobtained therefrom.

The production of molding grade resins from condensation polymers suchas polyesters, polycarbonates and polyamides, which are flame retardantand possess good mechanical properties is of considerable commercialimportance.

Halogenated materials are commonly used to impart flame retardance topolyesters and polyamides. Their use in such condensation polymers hasbeen hampered by the fact that HCl or HBr produced during processing bydecomposition of the flame retardant additive leads to hydrolsis anddegradation of condensation polymers. This hydrolytic degradation isparticularly severe at the high processing temperatures needed with thestiff-flowing aromatic polyesters and polycarbonates.

To greatly reduce the amount of halogenated additives needed for flameretardance, antimony oxide or other synergists are normally used.However, these synergists, while very effective in imparting flameretardance, greatly increase the hydrolytic and degradation process andalso reduce blend toughness by behaving as stress concentrators.

SUMMARY OF THE INVENTION

It has been found possible to greatly retard and minimize the abovedegradative process in condensation polymers by discouraging prematurephysical and chemical contact of the flame retardant synergist with theflame retardant under normal processing and molding conditions, whilestill allowing such needed interaction to occur at flame temperatures.This is accomplished by isolating the halogenated additive from thesynergist by either (1) encapsulating or imbedding the synergist inrubber particles or (2) covering the surface of synergist particles witha stable rubber film or layer.

One aspect of the invention is therefore directed to flame retardantresin compositions comprising

A. a condensation polymer selected from the group consisting ofthermoplastic polyesters, polycarbonates and polyamides;

B. an effective amount of a halogenated flame retardant additive; and

C. an effective amount of a flame retardant synergist of averageparticle size less than about 2 microns, wherein the particles of thesynergist are substantially occluded with a non-blocking rubber.

Another aspect of the invention is directed to articles molded from suchresin compositions and a third aspect of the invention is directed tothe process of preparing the resin compositions comprising

A. dispersing a flame retardant synergist of average particle size lessthan about 2 microns in a latex of a non-blocking rubber of averageparticle size in the range of about 0.05 to about 2 microns,

B. coagulating the latex to form a coagulum wherein the rubber particlessubstantially occlude the particles of flame retardant synergist,

C. recovering and drying the coagulum, and

D. melt blending and dispersing the coagulum in a thermoplasticcondensation polymer selected from the group consisting of polyesters,polycarbonates and polyamides containing an effective amount of flameretardant, to provide a dispersion of substantially occluded flameretardant synergist in a synergistically effective amount in thecondensation polymer.

THE PREFERRED EMBODIMENT

The thermoplastic condensation polymers suitable for the preparation ofthe resin compositions of the present invention are selected from thegroup consisting of polyesters, polycarbonates and polyamides.

Suitable polyesters are the condensation products obtained by reactionof glycols and diphenols with dicarboxylic acids. Typical glycols arethe alkylene glycols and the alkyleneoxy glycols in which the alkylenegroup may contain from 2 to 8 carbon atoms, such as ethylene glycol,tetramethylene glycol, hexamethylene glycol, cis- or trans-1,4-dimethylolcyclohexane and diethylene glycol. Typical diphenols(preferably condensed in the form of their diacetates or diesters ofother volatile acids prior to reaction with the dicarboxylic acid)include hydroquinone, resorcinol, bis(4-hydroxyphenyl)methane,1,1-bis(4-hydroxyphenyl)ethane, 1,2-bis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)propane, bis (4-hydroxyphenyl)sulfide,bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)ether, as well as thevarious diphenols such as 4,4'-diphenol and the dihydroxynaphthalenessuch as 2,5-dihydroxynaphthalene. Typical dicarboxylic acids includeisophthalic acid, terephthalic acid, 4,4'bibenzoic acid,bis(4-carboxyphenyl)ether, bis(4-carboxyphenyl)sulfide,bis(4-carboxyphenyl)sulfone, bis(4-carboxyphenyl)methane,1,2-bis(4-carboxyphenyl)ethane, 1,2-bis(4-carboxyphenoxy)ethane,hexahydroterephthalic acid, 5-t-butylisophthalic acid,5-chloroisophathalic acid, and the various naphthalene dicarboxylicacids such as 2,5-naphthalene dicarboxylic acid.

Suitable polycarbonates are the polycarbonates of diphenols exemplifiedby the diphenols set forth above.

Suitable polyamides are condensation products obtained by reaction of C₆to C₁₂ aliphatic diacids and C₆ to C₁₂ aliphatic primary diamines suchas polyhexamethylene adipamide (nylon 6,6), polyhexamethylene sebacamide(nylon 6,10) and polyhexamethylene dodecamide (nylon 6,12), or by thepolymerization of lactams such as ε-caprolactam (nylon 6), αpyrrolidone,piperidone, valerolactam, lauryllactam, etc.

The condensation polymer is of sufficient molecular weight to provideadequate mechanical properties to articles molded from the resincomposition of the present invention and preferably possesses a numberaverage molecular weight of at least about 10,000.

The halogenated flame retardant additive is selected from among the manysuch additives available to the practitioner of the art. Such additivesinclude halogenated diphenylethers containing from 6 to 10 chlorine orbromine atoms per molecule such as decabromodiphenylether; halogenatedaliphatic hydrocarbons such as the chlorinated parafins andhexabromocyclododecane; halogenated aromatic hydrocarbons such ashexabromobenzene and halogenated diphenyls containing from 6 to 10chlorine or bromine atoms per molecule such as decabromodiphenol; andhalogenated diphenyl carbonates containing from 6 to 10 chloride orbromine atoms per molecule such as 2,4,6-tribromodiphenyl carbonate anddecabromodiphenyl carbonate. The halogenated flame retardant additive isadded to the condensation polymer in sufficient amount to enhance flameretardance. Generally, from about 3 to about 15 weight percent based onthe weight of the total resin composition is added.

In order to maximize the effect of the halogenated flame retardantadditive, a flame retardant synergist, selected from the many suchadditives available to the practitioner of the art, is added to thecomposition. Such synergists include zinc oxide, zinc borate, ferrousand ferric oxides, alumina, antimony oxide and the like and are used ineffective amounts generally in the range of about 0.5 to about 5 weightpercent based on the weight of the total resin composition. Antimonyoxide is a preferred synergist. The flame retardant synergist is of fineparticle size such that the weight average particle size is less thanabout 2 microns and preferably less than about 0.1 micron. Such fineparticle sizes are readily obtained by milling or grinding techniqueswell known to those skilled in the art. Nyacol Inc., Ashland, Mass. is aconvenient source of colloidal antimony oxide sold as water dispersionsand pastes, the particle size of the antimony oxide being approximately15 millimicrons.

Although the flame retardant synergist greatly increases the degree ofhydrolytic degradation of the condensation polymers of the presentinvention when the polymers are melt blended with halogenated flameretardant and synergist, isolation of the flame retardant synergist fromthe flame retardant has now been found to reduce the degradation processvery effectively. Such isolation has been achieved by encapsulating orembedding the synergist particle in rubber particles or covering thesurface of the synergist particles with a rubber film or layer so thatthe synergist particles are substantially covered or occluded with thenon-blocking rubber. The term non-blocking rubber is used to connote acomposition comprising a three-dimensional network structure with aglass transition temperature below room temperature, particles of whichhave little tendency to flow together and coalesce into largenon-dispersible lumps at normal processing temperatures because of thepresence of a sufficient density of crosslinks or because the presenceof blocks or grafts or copolyblends which have a glass transitiontemperature sufficiently above the drying temperature to which thecoagulated latex may be subjected during the recovery of the occludedsynergist. Preferred non-blocking rubber compositions include homo- andcopolymers of monomers such as butadiene, isoprene and isobutylene andpolyblends and graft and block copolymers thereof of the type which areconventionally used in the rubber reinforcement of thermoplastic resins.Thus, homo- and copolymers of butadiene of a crosslink density whichwould not make them non-blocking may be rendered non-blocking by graftor block polymerization of monomers such as styrene, acrylonitrile ormethyl methacrylate. Such graft or block copolymers provide an advantagein that they aid ready dispersion of the occluded synergist in thecondensation product. The non-blocking rubber is preferably prepared byconventional methods such as by emulsion polymerization, suspensionpolymerization or mass polymerization. It can be obtained as an aqueouslatex of particle size in the range of about 0.05 to 2.0 microns, andmore preferably of particle size in the range of 0.1 to about 0.7micron. It may also be obtained by a mass or mass-suspension process ina particle size range of about 1 to 10 microns and more preferably inthe range of about 2 to 3 microns.

In one method of coating the particulate flame retardant synergist withnon-blocking rubber, the synergist in powder form is wetted with waterand dispersed in a latex of non-blocking rubber and the latex iscoagulated by any suitable means such as by freezing, by salt additionor by pH adjustment. Alternatively, an anionic or cationic aqueouscolloidal dispersion of the flame retardant synergist is mixed with asimilarly charged latex of non-blocking rubber and the latex isagglomerated or coagulated by any suitable means such as by freezing, bysalt addition or by adjustment of the pH. In another method a stream ofanionic aqueous colloidal dispersion of flame retardant synergist ismixed with a stream of cationic latex of non-blocking rubber to give acoagulum comprising flame retardant synergist particles coated withlatex particles. In yet another method, a stream of cationic aqueouscolloidal dispersion is mixed with a stream of anionic latex ofnon-blocking rubber. In a further alternative, a rubber monomer is addedto an aqueous colloidal dispersion of flame retardant synergist and ispolymerized by conventional free radical methods to form a coating ofpolymer on the particles of flame retardant synergist. The coating isthen rendered non-blocking by graft polymerization of a suitable monomersuch as styrene, acrylonitrile, or methyl methacrylate and the coatedparticles are agglomerated or coagulated by any suitable means such asby freezing, by salt coagulation or by adjustment of the pH. In stillanother alternative, the antimony oxide is suspended in a suspension ormass system comprising a rubber polymer and a monomer system containingone or more monomers selected from the group consisting of styrene,α-methyl styrene, and methyl methacrylate and optionally containingacrylonitrile or methacrylonitrile and the system is subjected tosuspension or mass polymerization.

The affinity of the flame retardant synergist for the occluding rubberin a mass or suspension polymerization system can be increased bytreatment of the synergist with a coupling agent prior to itsintroduction to the polymerization system. The coupling agent ispreferably an organosilane coupling agent containing an oleophilicgroup. Examples of such coupling agents include alkyl- andcycloalkyl-alkoxysilanes such as hexyltrimethoxysilane,octyltrimethoxysilane, dodecyltrimethoxysilane,octadecyltrimethoxysilane, dioctyldimethoxysilane,dioctyldiethoxysilane, cyclohexyltrimethoxysilane, and the like andepoxyalkyl- and epoxycycloalkyl-alkoxysilanes such as9,10-epoxyoctadecyltrimethoxysilane and3,4-epoxycyclohexyl-trimethoxysilane and the like. The amount ofcoupling agent used is sufficient to impart an oleophilic character tothe flame retardant synergist and is generally in the range of about 0.1to about 4 parts per 100 parts of synergist. The coupling agent isapplied to the synergist by any of the conventional methods for suchapplication such as by spray or by solution application.

The agglomerate or coagulum formed by the various methods of coating orencapsulating the flame retardant synergist comprises particles ofsynergist substantially coated with or occluded by non-blocking rubber.The agglomerate or coagulum is separated from the supernatant aqueousphase and is dried or vacuum dried at a temperature below the blockingtemperature of the rubber. It is then blended and dispersed by anysuitable means such as melt blending with the condensation polymer andthe halogenated flame retardant. The ratio of non-blocking rubber latexto flame retardant synergist is selected so that there is at leastsufficient non-blocking rubber to substantially cover the synergist.While the rubber serves to isolate the synergist from the halogenatedflame retardant, it also improves the toughness and tensile elongationof articles molded from the resin composition. The rubber fraction ofthe non-blocking rubber is preferably present in the range of about 2 toabout 15 weight percent based on the weight of the total resincomposition. Electron microscopy reveals that the bulk of the flameretardant synergist remains occluded by or embedded in the rubber phaseand thus has little opportunity to interact with the halogenated flameretardant which is preferentially dispersed or dissolved in thecondensation polymer, until the polymer is exposed to flamingconditions.

The thermoplastic vinyl addition polymers which may be convenientlyadded to the rubber occluded flame retardant synergist as ananti-blocking agent, diluent or dispersion aid may be any polymer with aglass transition temperature above room temperature such as polymers ofstyrene, α-methylstyrnee, acrylonitrile, methacrylonitrile, vinylacetate, methyl acrylate and methyl and ethyl methacrylate. Because oftheir relatively high glass transition temperature, homo- and copolymersof styrene, α-methylstyrene and methyl methacrylate and copolymers ofacrylonitrile are preferred. The thermoplastic vinyl addition polymercan be added in suspension or latex form to the dispersion of flameretardant synergist in the rubber suspension or latex prior toagglomeration or coagulation. Melt blending of this agglomerate orcoagulum with the condensation polymer leads to a fine dispersion in thecondensation polymer of the vinyl addition polymer containing the rubberoccluded flame retardant synergist. The vinyl addition polymer can actalso as a processing aid since it can reduce the melt viscosity of themolding resin and can be used advantageously for this purpose to providea total including grafted vinyl addition polymer of up to about 40weight percent based on the weight of the total resin composition.Excessive amounts may, however, interfere with the desired rubbercoating of the flame retardant synergist and/or with the agglomerationprocess. It is therefore, preferred to limit the amount of vinyladdition polymer including grafted vinyl addition polymer at theagglomeration step to no more than twice the weight of rubber component.If a larger amount of vinyl addition polymer is desired as a processingaid, it can be introduced separately in any convenient form for suchaddition, for example, as solid pellets and dispersed by melt blending.

In addition to the above described components, the resin compositions ofthe present invention can include additives such as colorants,plasticizers, stabilizers, hardeners, lubricants, reinforcing agents andthe like.

Blending of the components of the resin composition of the presentinvention is carried out in any convenient way, such as by dry mixingpellets or powder of the condensation polymer with the flame retardantand rubber-occluded synergist or by adding flame retardant andrubber-occluded synergist to molten condensation polymer. The variouscomponents and any other additives are preferably as free as possible ofwater. Mixing is preferably carried out in as short a time as needed toprovide a sufficiently intimate and uniform blend. Melt blending iseffected at a temperature selected for adequate melt viscosity butinsufficient to cause thermal degradation of the resin. The molten blendcan be extruded and cut up into molding compounds such as granules,pellets, etc. by conventional techniques.

The resin compositions can be used as molding resins and can be moldedin any equipment conveniently used for thermoplastic compositions attemperatures suitable for the particular molding resin composition,e.g., an Arburg machine with temperature in the range of about 250° toabout 350° C. and mold temperature about 100° to 150° C. can be used.Depending on the molding properties of the condensation polymer, theamount of the other components and the melt viscosity of the moldingresin, those skilled in the art will be able to make the conventionaladjustments in molding cycles to accommodate the composition.

The invention is further illustrated but is not intended to be limitedby the following examples in which parts and percentages are by weightunless specified otherwise.

EXAMPLE 1

This Example shows the preparation of rubber-occluded flame retardantsynergist from a finely divided powder of antimony oxide.

A finely divided antimony oxide of weight average particle size 1.6microns was wetted with water and added to an anionic latex containing40 weight percent of a polybutadiene latex grafted with 20 parts of aninterpolymer containing 70 percent styrene and 30 percent acrylonitrileper 100 parts of polybutadiene. The latex was stirred to provide auniform dispersion and to facilitate adsorption of the rubber on theantimony oxide. An anionic latex containing 40 weight percent of anα-methylstyrene acrylonitrile interpolymer (αMS:AN=70:30) was added tothe latex dispersion to provide a weight ratio of 1 part polybutadieneto 10 parts of styrenic interpolymer (PSAN+PαMSAN) and the blend wasstirred until the dispersion was again uniform. A small amount of latexcontaining Polygard, a rubber stabilizer and Ionol antioxidant toprovide 2 parts Polygard and 1 part Ionol per 100 parts polybutadienewas added and the mixed latices were coagulated by adding the blend to a4 percent aqueous solution of magnesium sulfate at 92° C. The finecoagulum was separated, washed with water to remove the salts and driedin vacuo. It was then blended with an amount of α-methylstyreneacrylonitrile interpolymer to give a ratio of styrenic interpolymer to"ungrafted" polybutadiene to antimony oxide of 22:8:1.

EXAMPLE 2

Example 1 was repeated to provide a rubber-occluded flame retardantsynergist comprising styrene acrylonitrile interpolymer, ungraftedpolybutadiene and antimony oxide in the weight ratio of 22:8:2.

EXAMPLE 3

This Example describes the preparation of rubber-occluded flameretardant synergist from a colloidal dispersion of synergist.

An aqueous colloidal dispersion of antimony oxide sold by Nyacol, Inc.,Ashland, Mass. under the trade name Nyacol A-1530, containing 30 weightpercent antimony oxide was added to an aqueous anionic latex containing40 weight percent of polybutadiene grafted with 20 parts of aninterpolymer containing 70 percent styrene and 30 percent acrylonitrileper 100 parts of polybutadiene and was stirred to provide a uniformblend. The procedure of Example 1 was then carried out to obtain a blendof rubber-occluded antimony oxide in an interpolymer of α-methylstyreneand acrylonitrile. The ratio of styrenic interpolymer to "ungrafted"polybutadiene to colloidal antimony was 22:8:1.

EXAMPLE 4

This Example sets forth the preparation of a resin compositioncomprising an aromatic polyester, a flame retardant and therubber-occluded antimony oxide of Example 1.

Finely divided decabromodiphenyl ether, DBDPE (5 parts by weight) wasdry blended with 30 parts by weight of the rubber-occluded antimonyoxide of Example 1 and 70 parts by weight of pellets of an aromaticpolyester of inherent viscosity 0.72 which was the condensation productof 2,2-bis(4-acetoxyphenyl)propane and an equimolar mixture ofisophathalic and terephthalic acids. The dry blend was further meltblended in a Brabender Plastigraph at 270° C. extruded and pelletized toprovide a molding resin composition. Inherent viscosity of the polyesterwas determined at 25° C. on a solution containing 0.5 g. polyester perdeciliter of solution. The solvent was a 60:40 blend of phenol andsymtetrachloroethane.

The resin composition was molded in an Arburg machine at 300° C. toprovide molded test samples. Measurement of physical properties wascarried out in accordance with the following methods: tensile strengthASTM D 638; Izod impact strength ASTM D 256; flame retardance UL-94ratings of Sept. 17, 1973. [Note: the UL-94 ratings are not intended toreflect hazards which may be presented by test materials under actualfire conditions.] Melt viscosity was determined on a Sieglaff-McKelveycapillary rheometer at 316° C. and a shear rate of 100 sec.⁻¹. The dataare presented in Table 1.

EXAMPLES 5-6

Resin compositions were prepared as in Example 4 with therubber-occluded antimony oxides of Examples 2 and 3, respectively. Datafor physical properties are presented in Table 1.

EXAMPLES 7-10

For comparative purposes, resin compositions comprising a polyblend of70 parts by weight of the polyisophthalate-terephthalate of Example 4,30 parts by weight of a blend of the styrene acrylonitrile interpolymerand styrene-acrylonitrile-polybutadiene graft of Example 1 containing 22parts by weight of styrene-acrylonitrile interpolymer and 8 parts ofpolybutadiene was prepared by the melt blending method of Example 4. Thepolyblend was further blended with flame retardants and synergists asfollows:

Example 7--100 parts by weight polyblend, 5 parts by weight DBDPE.

Example 8--100 parts by weight polyblend, 10 parts by weight DBDPE.

Example 9--100 parts by weight polyblend, 5 parts by weight DBDPE, 1part by weight of finely divided antimony oxide of weight averageparticle size 1.6 microns.

Example 10--100 parts by weight polyblend, 5 parts by weight DBDPE, 2parts by weight of finely divided antimony oxide of weight averageparticle size 1.6 microns.

Data for physical properties are presented in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    EVALUATION OF RESIN COMPOSITIONS COMPRISING AROMATIC POLYESTERS                                Izod                                                         Parts per 70 parts Polyester                                                                   Impact           UL-94 Flammability                          Molding    Antimony                                                                            Strength                                                                            Tensile                                                                            Elongation                                                                          Test - Sample thick-                        Resin DBDPE                                                                              Oxide joules/cm                                                                           MPa  %     ness 3.2 mm                                 __________________________________________________________________________    Example 4                                                                           5    1     1.4   59   25    V-0                                         5     5    2     1.1   59   15    V-0                                         6     5    2     2.3   59   59    V-0                                         7     5    --    2.5   59   56    Fail                                        8     10   --    2.0   --   --    V-1                                         9     5    1     0.9   --   --    V-1                                         10    5    2     1.0   --   --    V-0                                         11    --   --    2.9   59   65    Fail                                        __________________________________________________________________________     DBDPE = decabromodiphenyl ether.                                         

The data of Table 1 show that the introduction of decabromodiphenylether does little to improve flame retardance of the polyestercomposition (Example 11 vs. Example 7) and that the composition withantimony oxide to improve the flame retardance of the polyester causes asevere decline in impact strength (Example 11 vs. Examples 9, 10). Whenthe flame retardant synergist is occluded with polybutadiene graft, thedamage to impact strength is lessened while the improved flameretardance is maintained (Examples 4, 5 vs. Examples 9, 10), and thisdamage is further decreased when rubber-occluded colloidal antimonyoxide is used (Example 6 vs. Examples 4, 9). A further advantage of therubber-occluded colloidal antimony oxide is shown by the relativestability of the melt viscosity of the resin composition on prolongedheating in a capillary rheometer at 280° C. Greater preservation of meltviscosity on heating is indicative of reduced molecular weightdegradation of the polyester component. The rate of melt viscositychange with time at constant shear stress is shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        RATE OF DEGRADATION                                                           ON PROLONGED HEATING IN A RHEOMETER                                                      Melt viscosity at 280° C.                                              kilopoise at 200 sec-.sup.1                                        Example      5 Minutes        14 Minutes                                      ______________________________________                                        11           32               23                                              9            17               3.6                                             6            26               17                                              ______________________________________                                    

Reduced molecular weight degradation is further illustrated by the dataset forth in Table 3 for the inherent viscosity of the polyesterrecovered from molded samples of the polyester blends of Examples 4, 6,11 and 12 containing flame reretardant and flame retardant synergist.Example 12 comprises polyester, DBDPE and antimony oxide in the weightratio of 100:7:2 without rubber additive.

                  TABLE 3                                                         ______________________________________                                        EFFECT OF FLAME RETARDANT ADDITIVES                                           ON INHERENT VISCOSITY OF                                                      POLYESTER DURING THE MOLDING CYCLE                                                                       Inherent                                                                      Viscosity of                                                Parts per 70 parts Polyester                                                                    Recovered                                          Example    Rubber  DBDPE   Antimony Oxide                                                                          Polyester                                ______________________________________                                        4          8       5       1         0.56                                     6          8       5       1 (Colloidal)                                                                           0.63                                     11         8       None    None      0.62                                     12         None    5       1.4       0.42                                     ______________________________________                                    

The data show that the degree of degradation of molecular weight ofpolyester and polyeester containing occluded colloidal antimony oxide isalmost identical while a somewhat greater degree of degradation occurswith occluded particulate antimony oxide and a significantly greaterdegree occurs with polyester containing flame retardant and synergistunprotected by rubber.

EXAMPLE 13

A polycarbonate of 2,2-bis(4-hydroxyphenyl)propane is melt blended withdecabromodiphenyl ether and the rubber-occluded antimony oxide ofExample 3 by the method and in the proportions of Example 4. Improvedflame retardance is obtained in comparison with the polycarbonatewithout flame retardant and synergist. Improved impact resistance andpolymer stability is obtained in comparison with a compositioncomprising the same proportions of polycarbonate, DBDPE, antimony oxide,polybutadiene graft and copolymer of styrene and acrylonitrile, which isprepared by simple blending of the components without the step ofocclusion of antimony oxide in the polybutadiene graft.

EXAMPLE 14

A nylon 6,6 is melt blended with decabromodiphenyl ether and therubber-occluded antimony oxide of Example 3 by the method and in theproportions of Example 4. Improved flame retardance is obtained incomparison with the nylon 6,6 without flame retardant and synergist.Improved impact resistance and polymer stability is obtained incomparison with a composition comprising the same proportions of nylon6,6, DBDPE, antimony oxide, polybutadiene graft and copolymer of styreneand acrylonitrile which is prepared by simple blending of the componentswithout the step of occlusion of antimony oxide in the polybutadienegraft.

What is claimed is:
 1. A resin composition comprisingA. a thermoplastic polyester; B. an effective amount of a halogenated flame retardant additive; and C. an effective amount of a flame retardant synergist of average particle size less than about 2 microns, wherein the particles of the synergist are substantially occluded with a non-blocking rubber.
 2. A resin composition comprisingA. a thermoplastic polyester; B. about 3 to about 15 weight percent of a halogenated flame retardant additive; C. about 0.5 to about 5 weight percent of a flame retardant synergist of average particle size less than about 2 microns; D. about 2 to about 15 weight percent of a non-blocking rubber substantially occluding the particles of flame retardant synergist; and E. about 0 to about 40 weight percent of a thermoplastic vinyl addition polymer;wherein the weight percentages are based on the weight of the resin composition.
 3. The resin composition of claim 2 wherein the flame retardant synergist is selected from the group consisting of zinc oxide, zinc borate, ferrous and ferric oxides, alumina, and antimony oxide.
 4. The resin composition of claim 3 wherein the flame retardant synergist is of particle size less than about 0.1 micron.
 5. The resin composition of claim 4 wherein the flame retardant synergist is antimony oxide.
 6. The resin composition of claim 2 wherein the non-blocking rubber is selected from the group consisting of homo- and copolymers of butadiene, isoprene, and isobutylene.
 7. The resin composition of claim 2 wherein the thermoplastic vinyl addition polymer is selected from the group consisting of polymers of styrene, α-methylstyrene, acrylonitrile and methyl methacrylate.
 8. A resin composition comprising:A. a thermoplastic polyester; B. about 3 to about 15 weight percent of a halogenated flame retardant additive; C. about 0.5 to about 5 weight percent of an antimony oxide of particle size less than about 0.1 micron; D. about 2 to about 15 weight percent of non-blocking butadiene rubber substantially occluding the particles of antimony oxide; and E. about 0 to 40 weight percent of a thermoplastic vinyl addition polymer selected from the group consisting of polymers of styrene, α-methylstyrene, acrylonitrile and methyl methacrylate;wherein the weight percentages are based on the weight of the resin composition.
 9. An article molded from the resin composition of claim
 1. 10. An article molded from the resin composition of claim.
 2. 11. An article molded from the resin composition of claim
 6. 12. An article molded from the resin composition of claim
 8. 13. A process for preparation of a resin composition comprising a thermoplastic polyester, an effective amount of a flame retardant and an effective amount of a flame retardant synergist wherein the process comprises:A. dispersing the flame retardant synergist of average particle size less than about 2 microns in a latex of a non-blocking rubber of average particle size in the range of about 0.05 to about 2.0 microns; B. coagulating the latex to form a coagulum wherein the rubber particles substantially occlude the particles of flame retardant synergist; and C. recovering and dispersing the coagulum in the thermoplastic polyester containing the flame retardant.
 14. The process of claim 13 wherein the flame retardant synergist is selected from the group consisting of zinc oxide, zinc borate, ferrous and ferric oxides, alumina, and antimony oxide.
 15. The process of claim 14 wherein the non-blocking rubber is selected from the group consisting of homo- and copolymers of butadiene, isoprene, and isobutylene.
 16. The process of claim 15 wherein the average particle size of the latex of non-blocking rubber is in the range of about 0.1 to about 0.7 micron.
 17. The process of claim 16 wherein the flame retardant synergist is added to the latex of non-blocking rubber as an aqueous colloidal dispersion. 